In the Korean landscape, outdoor advertisements are one of things leaving much to be desired so local governments have been conducting continually signboard improvement projects. Hence, this study aimed to examine how colors of outdoor advertisements before and after the signboard projects changed through the analysis on the monochromatic and color combination characteristics, and color relation with structures. Research findings are as follows. Firstly, through the signboard improvement projects, the number of colors used for dominant⋅assort colors were limited and those in harmony with surrounding environments and structures were used. On the other hand, as for accent colors, various categories of colors were used to reflect characteristics by store so it shows that perceived unity and variation were given at sites simultaneously. Secondly, there was a change where we can find out a probability of the color scheme in colors used rather than increasing the number of colors used for one signboard. Thirdly, irritating color palettes and disorderly color schemes changed into those using a rich mid-tone of mid-brightness and chroma so visual stability was ensured. This research differentiates from precedent studies in that it analyzed individual characteristics of signboards in sections for signboard improvement projects and suggested a direction for signboard color planning to be pursued for overall harmony of the landscape. Besides, research findings identified characteristic changes in colors used so this research has significance in that they may be used as helpful reference when signboard improvement projects are conducted in other regions.